Project 4: Roles and Regulation of Mutant p53 and p63 Isoforms in Urothelial Development and Bladder Cancer Progression Carlos Cordon-Cardo, M.D., Ph.D. Cumulative observations by our group led us to hypothesize that the molecular processes by which p53 and p63 regulate urothelial differentiation are causally linked to their role in bladder tumor initiation and progression. Our main objective is to define the critical functions of p53 and p63-isoforms in urothelial development, bladder cancer initiation and progression. For this purpose, we will use state-ofthe- art molecular pathology and genetic approaches utilizing in vitro cell-based assays and in vivo mouse models, validating significant findings in human normal and tumor bladder tissues. The specific aims are: Aim #1. Comprehensive analysis of p53 and p63-isoforms during urothelial development. We discovered that p63 is essential for urothelial differentiation, and that p63-null mice developed an abnormal mono-cellular layer urothelium. Prelimianry data supports that this layer is constituted of